topic Re: sendmail configuration issue with non-standard SMTP port in Operating System - Linux

sendmail configuration issue with non-standard SMTP port

Debbie Fleith — Wed, 28 May 2008 15:03:11 GMT

I need to get sendmail configured to send emails from a Linux server through a mail server running on Port 8080.

What changes would I need to make to sendmail.cf or other files to make this work?

Re: sendmail configuration issue with non-standard SMTP port

Steven E. Protter — Wed, 28 May 2008 17:30:08 GMT

Shalom,

Inbound or outbound?

IF its outbound, you might just want to have iptables firewall do a bit of port forwarding.

Otherwise you need to change sendmail.mc and muse m4 to compile a new sendmail.cf

sendmail.cf is not human readable IMO, sendmail.mc is.

http://www.sendmail.org

SEP

Re: sendmail configuration issue with non-standard SMTP port

Debbie Fleith — Wed, 28 May 2008 17:32:40 GMT

I need this for outbound email. What specific rule would I add to the firewall?

Re: sendmail configuration issue with non-standard SMTP port

Ivan Ferreira — Wed, 28 May 2008 19:44:20 GMT

Please see:

http://wiki.xdroop.com/space/sendmail/smart+host+ports

Normally, your firewall won't block outgoing packets.

Re: sendmail configuration issue with non-standard SMTP port

Matti_Kurkela — Thu, 29 May 2008 16:04:45 GMT

I guess SEP had something like this in mind:

iptables -t nat -A OUTPUT -p tcp -d mail.server.ip.addr --dport 25 --to-destination mail.server.ip.addr:8080 -j DNAT

This redirects any outgoing TCP connection to the mail server's port 25 to the port 8080 instead. Connection tracking is automatically invoked to ensure any returning packets are modified too, so the applications at either end can work just as usual.

In the viewpoint of any program on this host, including Sendmail, that particular mail server is now effectively running on port 25, not 8080.

Of course, this is just one of the many ways to skin this particular cat...

Note that this is a "nat" rule, not the usual "filter" rule, so a simple "iptables -L" won't display it. You'll need to use "iptables -t nat -L" to see it.

MK